1. Technical Field
This invention generally relates to food crop storage structures. More particularly, it relates to a sunlight reducing cover for an intake or exhaust louver on a food crop storage building.
2. Background
There are a number of agricultural food products such as potatoes, onions, radishes, carrots, ginger root, artichokes, citrus crops, etc., which are placed into bulk storage after harvest and held from a few months to up to a year prior to processing. In general, the storage environment most suitable for holding these products with a minimum of rot, shrinkage, greening or other losses, is a relatively cool and very controlled environment. For purposes of this disclosure, the potato and potato storage parameters are used as an example, however it should be noted that the problems associated with potato storage environments, and the principals of the present invention, are equally applicable to the storage of onions, carrots, radishes, and other food products requiring a cool and controlled storage environment.
The potato tuber, when harvested from the ground, is a living, respirating organism. The potatoes are dug from the ground and hauled in trucks, in bulk, to a storage facility where they are piled by means of movable conveyor belts, into piles 14 feet to 22 feet high atop of ventilation pipes or ducts. The typical potato storage in use today ranges in size from 9,000 square feet of earthen or concrete floor space to 65,000 feet of earthen or concrete floor space, and will hold between 2,500 tons to 40,000 tons of potatoes. Since these potatoes are living, respirating organisms, there is approximately 2 BTU's per ton of potatoes, per day, of heat generated by the dormant potatoes, or, between 5,000 BTU's to 80,000 BTU's per day of heat generated. Thus, in temperate weather conditions, the problem is not one of keeping the potatoes warm, but rather one of keeping them cool.
In general, there are two means of cooling potatoes in common use today. The first is generally described as the ventilation system, which uses outside ambient air and is suitable for holding potatoes in storage until late spring when the thermal load on the building from the potatoes within and the outside atmosphere increases to the point where a suitable storage environment can no longer be maintained. Where storage is designed to hold potatoes into hot summer months, refrigeration systems are added to the ventilation to provide supplemental cooling.
The prior art ventilation system is similar to that seen in FIG. 1. It includes a primary air recirculation system wherein cool humid air is blown into ventilation ducts positioned at the bottom of the potato pile. Air coming in through the ventilation ducts is distributed through vent holes in the pipes and flows up through the pile of potatoes into a return air plenum, or it is discharged directly to the outside atmosphere through exhaust louvers. The return air louver is a recirculation louver which returns the air to the ventilation fans in the supply air plenum. The return air louver controls the amount of air which flows out the exhaust louver to the outside atmosphere.
Also provided is an outside air intake louver which is used to supply cool, fresh air to the ventilation fans. A control system is provided which monitors the discharge air temperature supply to the potato pile in the supply air plenum and a second sensor monitors outside air temperature. Thus, in relatively moderate temperature conditions when the outside air temperature is below the desired storage temperature, the outside air louver is opened, either partially or fully, to provide a mixture of cool outside air with warmer inside air in the return air plenum, to provide potatoes with desired air temperature and control temperature within the storage. For longer term storage, refrigeration systems are provided to cool the return air and the outside air intake louvers are closed.
It is important that the intake and exhaust louvers be activated simultaneously, or at least coordinated to prevent over pressure or excessive thermal loss. This is usually accomplished by a relatively complex control system between the intake and exhaust louvers.
As a result of this complex control system, the intake and exhaust louvers can be opened for cycles lasting from as long as 12 to 24 hours. These long cycles when the louvers are opened for extended periods of time, allow for significant amounts of visible light to infiltrate the storage building. Light infiltration into the storage building is an undesirable consequence of the requisite open cycles of the intake and exhaust louvers. As a result of exposure to visible light, a green color appears in the area immediately beneath the skin of a potato. This phenomena is generally referred to as potato greening.
The greening is the manifestation of chlorophyll formation by the potato tuber in response to the exposure to visible light. When potatoes are in storage, the primary source of exposure to light is through the intake and exhaust louvers during the cycles designed to control the temperature of the storage building. The economic importance of potato greening lies in the lack of marketability of such potatoes, in part due to the association of greened potatoes with bitter taste and to the suspicion of poisonous substances being present. The best method for preventing greening is to keep the potatoes away from visible light.
In order to reduce the amount of visible light that infiltrates the storage building, hoods are installed on the exterior of the building over the intake and exhaust louvers. The hoods provide a shaded area over the intake and exhaust louvers to decrease the amount of visible light that infiltrates the storage building. Although the hoods reduce the amount of visible light that infiltrates the building, there are both management problems associated with the use of shade hoods and inherent design problems with the hoods.
The first problem involves ice formation associated with the use of shade hoods. The exhaust air leaving the building is at an approximate 90% relative humidity, in cool weather this places the dew point and the ambient temperature of the air leaving the storage building in very close range. Because of the shade provided by the hood, these conditions allow ice to form inside the hood during cool weather. This ice formation interferes with the functioning of the louvers and prevents the intake and exhaust louvers from functioning in concert to provide the controlled environment necessary in the food crop storage building.
Another problem with using shade hoods over the louvers is dirt build up. During rainy weather, the hood provides an environment where eddy currents of air bring dust and wet condensate in contact with each other, creating a dirt and mud problem in the area of the louvers. The dirt and mud build up can be significant, often to the extent of fouling the louvers and, again, disrupting control of the potato storage environment.
The size of the hoods also can be a problem. In certain geographical regions, large hoods are susceptible to wind damage. Gusts of wind cause movement inside the hoods, which increases over time. The wind-generated movement inside the hoods can result in stress fractures and ultimately in structural failure of the shade hoods.
The problems of ice formation and dirt fouling associated with the use of shade hoods is compounded by the fact that, frequently, food crop storage buildings are remotely located and consequently are checked infrequently. As a result of the remote locations, the potatoes can be housed in the storage units for extended periods of time without discovery of any problem. It is, therefore, important to have a system with a high degree of reliability that reduces the amount of light infiltration and allows proper louver function.
A useful shade hood must be of a reasonably large dimension in order to shade the louvers on the food crop storage buildings. An inherent disadvantage of the large dimensions of the shade hood is that an undesirable amount of visible light is still able to enter the building through the louvers because light is able to impinge on the hood and reflect back at the building and through the louvers.
What is still needed is a means for reducing potato tuber exposure to visible light when the intake or exhaust louvers are open. It is, therefore, an object of the present invention to provide a means for reducing visible light infiltration into a food crop storage building, and thereby reduce the amount of greening in potato tubers and the associated economic loss.
It is an additional object of the present invention to provide a sunlight reducing cover for intake and exhaust louvers on a food crop storage building that reduces the amount of reflected light that is able to infiltrate the building.
It is a further object of the present invention to provide a sunlight reducing cover for the intake and exhaust louvers on the food crop storage building that decreases the likelihood of ice formations or dirt fouling of the intake and exhaust louvers.